The present invention relates to low pressure delivery systems for cryogenic liquids, and discloses a system wherein the delivery of a single-phase liquid is accomplished by gravity.
One application to which the present invention is particularly suited is the injection of cryogenic liquids into aluminum cans. Aluminum is desirable, because of its relatively low cost, as a storage medium for food and beverages. However, except for aluminum cans which contain a carbonated liquid, creating significant pressure in the can, aluminum cans cannot be arranged in stacks. The weight of the stack literally crushes the cans near the bottom of the stack.
One way of compensating for the inherent weakness of aluminum cans is to inject a small amount of a cryogenic liquid into the can before the can is sealed. As soon as the cryogenic liquid is introduced into the can, the liquid vaporizes. Because the volume of a cryogen in the gaseous phase is several hundred times the volume occupied by the corresponding liquid, there is a substantial pressure buildup inside the can, which enables the can to withstand strong external pressures.
The apparatus used to fill aluminum cans with cryogenic liquids must be able to process a large number of cans in a very short time. The filling of such cans must be done by machine, and the machinery is designed to handle precisely measured, small amounts of cryogenic liquid. It is therefore necessary to provide the cryogenic liquid at a precisely-controlled low pressure. Any error in the pressure of the liquid becomes greatly magnified when the liquid vaporizes, because of the large expansion factor.
Cryogenic liquids are typically stored in cylinders at very high pressures, of the order of 25 psi, or even 100 psi. It is one object of the present invention to withdraw a cryogenic liquid from such a high-pressure source, and to deliver the liquid at a precisely-controlled low pressure. Although the invention has been described with reference to the art of filling aluminum cans, it is understood that the invention can be used in any other context requiring delivery of cryogenic liquids at controlled low pressures.
Various methods have been known for producing a stream of cryogenic liquids. One example is shown is U.S. Pat. No. 4,059,424. The latter patent provides apparatus for controlled supply of cryogenic liquids, the apparatus including a separate phase-separator, in addition to the main container. Another example is U.S. Pat. No. 4,192,147, which shows another cryogenic liquid delivery system wherein the liquid is withdrawn from the bottom of a container.
The present invention accomplishes the object of providing a stream of cryogenic liquid, at a controlled low pressure, in a manner which is efficient and inexpensive. The present invention does not require the use of a separate phase separator. The invention yields a substantially single-phase liquid which is ready for immediate use.